Field of the Invention
The present invention relates to an image reading apparatus, e.g., a scanner, which is configured to read an image (hereinafter referred to as “original image”) of an original.
Description of the Related Art
An image reading apparatus is provided to an image forming apparatus, e.g., a copier or a multifunction apparatus, and is used to read an original image in copying or facsimile transmission. Moreover, the image reading apparatus may be connected to an information processing apparatus, e.g., a personal computer, and be used as a scanner. The image reading apparatus may include an original conveying apparatus, e.g., an automatic document feeder (ADF). The image reading apparatus including the original conveying apparatus is configured to continuously take in originals from the original conveying apparatus one by one, and to continuously read original images efficiently while conveying the taken-in originals. The image reading apparatus can efficiently read the original images by continuously taking in the originals from the original conveying apparatus.
To read an original image, the image reading apparatus irradiates an original being conveyed with light, and receives reflected light from the original. The image reading apparatus converts the received reflected light into an electric signal to generate image data representing the read original image. The image reading apparatus reads the original image by irradiating the original with light assuming that a direction perpendicular to a conveying direction of the original is amain scanning direction. When the original is conveyed with inclination with respect to the main scanning direction, the image reading apparatus reads the original image in an inclined state. In order to correct the inclination of the original image, there is proposed a technology for detecting an inclination amount of an original being conveyed to perform inclination correction.
In Japanese Patent Application Laid-open No. 2013-123119, there is proposed an image reading apparatus capable of detecting, with precision, edge portions of an original image that are used in the detection of the inclination amount of the original image. The image reading apparatus of Japanese Patent Application Laid-open No. 2013-123119 is configured to detect the inclination amount of an original image by reading an image of a wider area than the original and inferring the area of the original image from the result of the reading, based on the size of the original and on the result of detecting the edge portions of the read image.
In the case where specks, smudges, and the like are adhered to the background portion of an image reading apparatus which is outside the area of an original at a point where an original image is read, the image reading apparatus erroneously reads the specks, smudges, and the like in the background portion as an image (hereinafter referred to as “speck image”). The image reading apparatus conducting original image edge portion detection from a read image that contains a speck image may mistake the speck image for an edge portion of the original image. Misidentification of the original image edge portion hinders the accurate detection of the inclination amount of the original image. This problem is addressed by an image reading apparatus of U.S. Pat. No. 8,018,629 in which a speck image is regarded as an image with no density changes, and the determination of an original edge is controlled so as to exclude a spot where the speck image is located from the determination.
Reading of an image of an original that is being conveyed generally creates a considerable amount of paper dust. Paper dust moves around due to static electricity and air currents, and therefore forms floating specks instead of being fixed in one place. The density of a speck image in which floating specks are read is inconstant unlike a speck image of fixed specks. In addition, a speck image of floating specks may move location. It is therefore difficult for the related art to exclude a speck image of floating specks from the edge portion determination, which leads to the chance of erroneously detecting a speck image of floating specks as an edge portion.